In recent years, every electric apparatus is controlled by an inverter circuit in view of environmental protection in order to promote energy saving and to pursue higher efficiency. In the automobile industry, among others, a hybrid car (hereinafter referred to simply as HEV) driven with an electric motor and an engine has been introduced in the market, so that techniques pursuing environmental friendliness, energy saving, and higher efficiency are actively developed. Since the market demands maintenance-free products, HEV thus tends to adopt a metalized film capacitor that features an ultra long life.
The electric motor to be used in HEV works at as high as several hundreds volts, so that a metalized film capacitor having the following electric characteristics is strongly demanded: a high withstand voltage, capability of being charged and discharged with a large amount of current, a large capacitance, and a small loss at a high withstand voltage. To meet this requirement, a case mold type capacitor has been developed and commercialized. This case mold type capacitor is formed of multiple metalized film capacitors connected in parallel to each other with a bus bar and accommodated within a case, into which mold-resin is injected for fixing the film capacitors within the case.
FIG. 7 shows a structure of a conventional case mold type capacitor. This capacitor includes multiple capacitor elements 41, a pair of bus-bars 43, and case 45. Each of capacitor elements 41 is formed by winding two metalized films into a flat shape. Each of the films is made by depositing metal on single side of dielectric polypropylene film. Each of capacitor elements 41 includes metalized contact electrodes 42, working as electrodes, on both ends along the width direction of the metalized films. Electrodes 42 are formed by spraying zinc. Each of bus-bars 43 made of elongated copper connects the metalized contact electrodes 42 disposed on the ends of multiple capacitor elements 41 together. Each of bus-bars 43 includes electrode terminal 44 for external connection, and they are unitarily formed by bending. Case 45 is made of polyphenylene sulfide. Multiple capacitor elements 41 are arrayed in a line with their flat faces solidly contacted with each other along the same direction within case 45. Metalized contact electrodes 42 are provided to both the ends of each of capacitor elements 41, and they are roughly flush with each other on either ends respectively, and ones of electrodes 42 are disposed on an opening side and others of electrodes 42 are disposed on a bottom side of case 45. Bus-bars 43 connect the ones of electrodes 42 on the opening side of case 45 and the others of electrodes 42 on the bottom side of case 45, respectively. Electrode terminals 44 are disposed outside case 45. Case 45, in which multiple capacitor elements 41 and bus-bars 43 are disposed, is filled with sealing member, e.g. with epoxy resin 46, at empty spaces (the shaded area in FIG. 7 represents parts of the sealing member) for increasing reliability such as moisture resistance.
The structure discussed above allows increasing the capacitance as well as decreasing the number of components of conductive members for connecting the metalized contact electrodes 42 together. As a result, a wiring distance for connecting capacitor elements 41 together in parallel can be shortened. The foregoing case mold type capacitor is disclosed in, e.g. Patent Literature 1.
FIG. 8 shows another structure of the case mold type capacitor. In FIG. 8, multiple metalized film capacitors are disposed in parallel to each other, and the electrodes of respective capacitor elements are connected to each of bus-bars. Each of capacitor elements 1 includes end-face electrodes 2 at both ends thereof. Capacitor elements 1 are film capacitors, and end-face electrodes 2 are formed of metalized contacts. Three capacitor elements 1 are arrayed in parallel to each other and perpendicularly with respect to the direction of the pair of end-face electrodes 2, whereby capacitor element array 10A is formed. Another capacitor element array 10B having the same structure as array 10A is disposed adjacent to and in parallel with array 10A, whereby capacitor elements group 10C is formed.
First flat electrode 11 is disposed roughly in parallel with the arraying direction (the arraying plane) of capacitor elements 1. Second flat electrode 12 is disposed outside and roughly in parallel with the first flat electrode 11. In other words, second flat electrode 12 is located opposite to capacitor elements group 10C with respect to first flat electrode 11. First flat electrode lland second flat electrode 12 are made of copper and shaped like a rectangular plate, and they have quadrangular openings 13 and 14 at their centers respectively. Openings 13 and 14 extend along capacitor element arrays 10A and 10B respectively. Opening 13 of first flat electrode 11 is greater than opening 14 of second flat electrode 12 both in width and length.
End-face electrodes 2 located inside capacitor element arrays 10A and 10B are connected to the rim of opening 14 of second flat electrode 12 with lead terminals 3B running through opening 13 of first flat electrode 11. End-face electrodes 2 located outside capacitor element arrays 10A and 10B are connected to both outer sides (lateral ends) of first flat electrode 11 with lead terminal 3A. Lead terminals 3A and 3B are made of, e.g. copper tape having a length of approx. several mm (not longer than 10 mm) to minimize the inductance. Lead terminals 3A and 3B can be integrally formed with end-face electrodes 2. The foregoing connecting structure allows connecting all of capacitor elements 1 in parallel to each other between first flat electrode 11 and second flat electrode 12.
Insulating paper or insulating film (not shown) is inserted between capacitor elements group 10C and first flat electrode 11, and between first flat electrode 11 and second flat electrode 12. This structure allows placing capacitor elements group 10C, first flat electrode 11, and second flat electrode 12 as close as possible to each other. This unit thus structured is housed within the case and then sealed with resin, e.g. epoxy resin, whereby the case mold type capacitor is completed. This capacitor has an electrostatic capacitance ranging from several hundreds μF to several thousands μF, and an inductance ranging from several nH to several tens nH, so that this capacitor is useful as a smoothing capacitor or the like of an inverter.
Since capacitor elements group 10C is molded with molding resin in the case, the case mold type capacitor is excellent in mechanical strength, heat resistance, and water resistance. This capacitor is thus highly reliable. The case mold type capacitor discussed above is disclosed in, e.g. Patent Literature 2.
However, when the case mold type capacitor shown in FIG. 7 is used in HEV or an electric vehicle, it cannot satisfy the electric characteristics such as low loss at high withstand voltage. On top of that, the greater thickness of molded resin may incur cracks or breakages in the capacitor case or the molded resin due to thermal shock supposed to occur in the vehicle.
The case mold type capacitor shown in FIG. 8 satisfies the electric characteristics of low loss at high withstand voltage; however, this capacitor needs complicated connections between end-face electrodes 2 and flat electrodes 11, 12 of capacitor elements 1. In particular, lead terminal 3B runs through opening 13 of first flat electrode 11 for connecting end-face electrode 2 located inside to the rim of opening 14 of second flat electrode 12. This connection causes a problem of insulation reliability between end-face electrode 2, lead terminal 3B and first flat electrode 11.
On top of that, here is a common problem: when two or more kinds of capacitors are arrayed along the same direction, and their end-face electrodes 42 or 2 are arrayed along the same direction, the metalized films for those capacitors should have approx. the same width. This limitation makes it difficult to find performance and shape optimum to each one of two or more kinds of capacitors.